"Mana gaun terkecil yang Anda jual?"

Translation: Which is the smallest dress that you sell?

[donny309620]

"Mana" = "where". "Which" = "yang mana". Therefore, the English translation in this case should be "Where is the smallest dress that you sell?"

[Rick392366]

mana = which
di mana = where

[AndyBirtwistle]

Where is the smallest dress that you sell is sure acceptable?

[Diponegoro57]

Without any context to indicate that it is location that is being asked about, no ... the primary meaning of 'mana' as a question word is 'which'. 'Di mana' is 'where', although I think that can be shortened to 'mana' once it has been already established that the focus is on the location.